Infrared radiation source

ABSTRACT

An infrared radiation source having a plurality of turns of ceramic-coated platinum wire wound on a cylindrical dielectricceramic rod. The circumference of this structure is coated with a high emissivity paint which increases its infrared emissivity at high temperatures. The coated rod is coaxially supported in and is insulated from a truncated conical reflector. The ends of the wire are connected through an AC line voltage stabilizer comprising a resonant transformer to an AC voltage source.

'4 United States Patent 72] Inventor More Gmunner Sunnyvale, Calif. [21] Appl. No. 878,291 [22] Filed Nov. 20, 1969 [45] Patented Aug. 31, 1971 [73] Assignee Sylvanll Electric Products Inc.

[54] INFRARED RADIATION SOURCE 1 Club, 3 Drawing l ke. [52] 1.1.8. C1. 219/553, 219/347, 219/354, 219/355, 219/536 [51] Int. Cl. 1105b 3/10 [50] FieldotSearch 219/553, 552, 411, 405, 353, 354, 347, 355, 536-537; 338/364, 365, 302

[56] References Cited UNITED STATES PATENTS 2,303,873 12/1942 Anderson 219/354 2,413,043 12/1946 Ganci 338/265 2,497,676 2/1950 Lashells 219/354 X 2,745,940 5/1956 Stroh 219/354 X 3,242,314 3/1966 219/347 FOREIGN PATENTS 487,460 10/1952 Canada 219/354 512,019 8/1939 Great Britain 219/355 Primary Examiner-Volodymyr Y. Mayewsky Attorneys-Norman J. OMalley, Russell A. Cannon and John F. Lawler ABSTRACT: An infrared radiation source having a plurality of turns of ceramic-coated platinum wire wound on a cylindrical dielectric-ceramic rod. The circumference of this structure is coated with a high emissivity paint which increases its infrared emissivity at high temperatures. The coated rod is coaxially supported in and is insulated from a truncated conical reflector. The ends of the wire are connected through an AC line voltage stabilizer comprising a resonant transformer to an 1 AC voltage source.

PATENT-ED Aucsl 12m 3,602,693

INFRA RED RADIATION SOURCE J INVENTOR MARC GROUNNER IE 2| fl//A/;M

" AGENT INFRARED RADIATION SOURCE This invention relates to'sources of electromagnetic radiation and more particularly to a signal source for generating in-' frared radiation. 7

One of the most widely used sources of infrared radiation is the Nernst glower. It comprises an electrically conductive cylindrical ceramic rod having platinum wires connected to opposite ends thereof. The rod is preheated until it is sufficiently electrically conductive to pass an AC current which electrically heats the rod to higher temperatures. The resistance of the rod has a negative temperature coefficient and requires special regulation of the driving power supply to maintain the temperature of the rod, and therefore the intensity of the infrared radiation, relatively constant. The Nernst glower also requires a large driving current and therefore consumes large amount of electrical power, and has a low emissivity (the ratio of the radiation emitted by a surface to the radiation emitted by a black body radiator at the same temperature and under similar conditions). An object of this invention is the provision of a relatively simple and low cost source of midband infrared radiation requiring only a small amount of input electrical power.

This invention will be more fully, unde1stood from the following description of a preferred embodiment thereof which is illustrated in the accompanying drawings in which:

FIG. 1 is a plan view, partially in section, of an infrared radiation source embodying this invention,

FIG. 2 is an enlarged perspective view, partially in section, of the heater element of FIG. 1; and

FIG. 3 is a schematic diagram of the electrical circuit for energizing the source shown in FIG. 1.

Referring now to FIG. 1, an infrared radiation source 5 cmbodying this invention comprises a heater element 8 rigidly mounted in a support assembly 10, a reflector assembly 11 and an apertured plate 12. Assemblies 10 and 11 and plate 12 are supported in spaced relationship on base plate 14. Support assembly 10 comprises a flange 16 having an aperture 17 therein and a tubular member 18 having a shoulder 19 formed on one end thereof. Flange 16 is secured to the base plate by screws 20. Tube 18 is secured to flange 16 by screws 21.

Reflector assembly 11 comprises a flange 25 having an aperture 27 therein and a truncated cone 28 having a mirrorlike inner surface 29. A plurality of brackets 30 are brazed to the outer surface of the cone at the base thereof. The cone is secured to flange 25 by screws 31 extending through the flange and brackets 30. Flange 25 is secured to base plate 14 by screws 32 so that the apex end of the cone is spaced from flange 16.

Plate 12 is rigidly secured to the end of the base plate by screws 33. Flanges l6 and 25 and plate 12 are mounted on the base plate so that the apertures 17, 27 and 34 and the cone are coaxial with the axis X-X. A window 35 which covers the aperture 34 is secured to plate 12 by disc 36 and screws 37. The window may be made of PEP Teflon which has low loss to infrared signals.

Referring now to FIG. 2, the heater element 8 comprises a cylindrical ceramic tube 40 on which a plurality of turns of ceramic-coated platinum wire 41 are wound. Tube 40 is preferably made of a dielectric material such as a high alumina ceramic which is cured before the wire is wound on it. The coated wire '41 comprises a core wire 42 of commercial grade platinum that is coated with a ceramic insulation. The coated wire is wound around the tube when the insulation is in the uncured state. Adjacent turns of the coated wire are wound in close contact with each other over a major portion of the length of the tube. At the end 43 of the tube the wire is returned through the bore 44 to the other end 45 thereof.

After the coated wire is wound on tube 40 the tube and wire are placed in an oven and the temperature thereof is gradually raised to l,050 C. over a time interval of 4 hours. The heater is then baked in air at l,050 C. for 10 minutes to cure the ceramic insulation. After the insulation is cured lead wires 46 and 47 are wound around the end 45 of the tube with the turns thereof spaced apart. The insulation is removed from each end of the coated wire to expose the ends 42a and 42b of the core wire which are spot welded to each of the turns of lead wires 46 and 47, respectively. The lead wires may, by way of example, be made of nickel. A i v The closely wound turns of coated wi'r'e41 are then dipped in a bath of high emissivity paint such as Lithoid which is manufactured by Industrial Infrared, Sharon, Penna, and is allowed to air dry under an infrared lamp. The lead wires are then connected to a source of AC current which is employed to electrically heat the wire to 200 C. for 10 minutes. The coated wire is again dipped in high emissivity paint and air dried under an infrared lamp. The lead wires are again connected to an AC current source and the wire is gradually heated to 200 C. and held at that temperature for 10 minutes. The wire is then gradually heated to l,000 C. where it is held for 20 minutes to cure the high emissivity coating.

After the coating is cured, the tube is coaxially supported with the end 45 thereof in a cylindrical mold (not shown). The mold is filled with a ceramic spark plug cement such as Sauereisen (manufactured by Sauereisen Cement Company, Pittsburgh, Penna.) which dries to form a rigid dielectric plug 48 supporting the tube and the leads 46 and 47 in spaced relationship.

In order to mount the heater element 8 in the assembly 10, the base plate 14 and structure secured thereto are oriented with the apex end of the reflector 28 in a vertical position. The heater 8 is passed through the aperture 17 and the cone until the face 49 of the dielectric plug contacts flange 16. The heater element and the cone are coaxially aligned with the axis X-X with a mandrel (not shown). The heater element 8 is then rigidly secured in assembly 10 by filling the tube 18 with ceramic cement 54. After the bonding cement 54 dries, the alignment mandrel is removed and a cover (not shown) is attached thereto.

In order to produce a beam of infrared radiation, the radiation source 5 is connected through a variable resistor 55 to one of the windings of an AC line voltage stabilizer 56 which is energized by a source 57 of AC voltage, see FIG. 3. The stabilizer comprises a resonant transformer having a tertiary winding 58 resonant with an electrolytic capacitor 59. The impedance provided by resistor 55 may be varied to control the amount of current applied to source 5. The temperature of the wire 41 and the intensity of the infrared radiation produced by the radiation source are both functions of the amount of current passed by the heater wire 41. When the heater element 8 is energized, the cone produces a dispersive beam of infrared radiation which is converted to an essentially cylindrical beam of IR radiation over a short distance.

By way of example, an embodiment of this invention which was built and tested had the following dimensions:

Heater Element 8 Tube 40 Inner diameter 0.43 inch Outer Diameter 0.067 inch Coated wire 41 diameter 0.003 inch 1 Core wire 42 diameter 0.002 inch I Length A l inch Number of turns in A 300 A 'High emissivity paint Lithoid Cone 28 Length B i 0.4 inch Apex half-angle 0C 45 Aperture 17 diameter 0.09 inch Aperture 27 diameter 0.88 inch Aperture 34 diameter 0.75 inch The constant voltage transformer of AC line voltage stabilizer 56 was connected to a l 15-volt AC source. The infrared source had a SO-volt drop across it at 0.3 amps. thus consuma plurality of closely spaced turns of ceramic coated wire wound on said tube over a portion of the length thereof, the ends of said wire terminating adjacent the same one end of said tube,

a coating of high emissivity type material over said closely wound turns of ceramic-coated wire for increasing the infrared radiation of said wire at high temperatures,

electrically nonconductive means for dielectrically supporting said tube at said one end thereof,

a truncated cone having an inner surface which is optically reflective, the apex end of said cone being proximate said dielectric supporting means,

means coaxially supporting said tube in said cone with said portion of said tube extending over the axial length of and beyond said truncated cone,

a plate which is opaque to infrared radiation adjacent to and axially spaced from the other end of said tube, said plate having an aperture therein coaxial with said cone for.

producing a substantially cylindrical beam of infrared radiation,

an alternating current line voltage stabilizer responsive to the output signal for producing a stabilized AC voltage, said stabilizer including a resonant transformer, and

means for electrically connecting the output of said stabilizer to the ends of said wire, said connecting means comprising a variable resistor connected in series between said stabilizer and said wire for limiting the magnitude of the AC current passed thereby. 

1. An infrared radiation source responsive to an output signal from an alternating current (AC) power supply for producing infrared radiation, comprising a tube of electrically nonconductive ceramic material, a plurality of closely spaced turns of ceramic coated wire wound on said tube over a portion of the length thereof, the ends of said wire terminating adjacent the same one end of said tube, a coating of high emissivity type material over said closely wound turns of ceramic-coated wire for increasing the infrared radiation of said wire at high temperatures, electrically nonconductive means for dielectrically supporting said tube at said one end thereof, a truncated cone having an inner surface which is optically reflective, the apex end of said cone being proximate said dielectric supporting means, means coaxially supporting said tube in said cone with said portion of said tube extending over the axial length of and beyond said truncated cone, a plate which is opaque to infrared radiation adjacent to and axially spaced from the other end of said tube, said plate having an aperture therein coaxial with said cone for producing a substantially cylindrical beam of infrared radiation, an alternating current line voltage stabilizer responsive to the output signal for producing a stabilized AC voltage, said stabilizer including a resonant transformer, and means for electrically connecting the output of said stabilizer to the ends of said wire, said connecting means comprising a variable resistor connected in series between said stabilizer and said wire for limiting the magnitude of the AC current passed thereby. 